should probably be considered
an “exotic” because it costs
approximately 80 times as much
as an FKM O-ring. And while it
will raise the allowable working
temperature to 275 °C, as a prac-
tical matter, most users intending
to work at this temperature level
would be well advised to choose
a closure with a flat PTFE gasket
and a 350 °C temperature limit.
Other exotic O-ring materials are
available, and there are economi-
cally priced materials such as
ethylene-propylene that will
resist some materials that cause
FKM to fail, with only slight sacri-
fices in operating temperatures.
Contained Flat Flexible
Graphite Gaskets for
Temperatures to 600 °C
For operating temperatures
above 350 °C, Parr uses a flexible
form of graphite, called Grafoil
®
,
which has proven to be an excel-
lent high temperature sealing
material. It consists of flex-
ible layers of graphite bonded
together to produce a gasket that
is almost as easy to seal as a flat,
PTFE gasket, but with an almost
unlimited temperature range and
excellent chemical resistance.
Parr has converted all of its
standard designs to accept a
flat, Grafoil gasket whenever
operating temperatures above
350 °C are required, replacing
the metal gaskets formerly used
for high temperatures. These
flexible graphite gaskets are held
in grooves identical to the ones
used for PTFE gaskets and sealed
with the same split-ring closures.
This makes it possible to sub-
stitute a PTFE gasket whenever
the vessel is to be used at tem-
peratures below 350 °C. Grafoil
gaskets are reusable, but their
service life is shorter than can be
obtained with a PTFE gasket.
Metal Gaskets
Metal gaskets have trad
itionally been the only gaskets
available for use at temperatures
above 350 °C. Parr has designs
for diamond cross-section metal
gaskets which can be furnished
for special applications, but we
would recommend the flexible
graphite gaskets described above
for most applications.
Trademarks of Sealing Materials
A number of gasketing materials have so dominated their product categories that their Trade Names
have become more common than the actual material designation itself. In an attempt to respect the
value of these Trade Names and their proper usage and to minimize the disruptions in our descriptions,
we have adopted the following generic material descriptions and designations for use in this catalog.
Where available we have selected the ASTM material designation.
Common
or Trade Name
Material
Designation
Viton
®
fluoroelastomer
FKM
Kalrez
®
perfluoroelastomer
FFKM
Teflon
®
tetrafluoroethylene polymer
PTFE
Grafoil
®
flexible graphite
FG
Viton
®
, Kalrez
®
,Teflon
®
are Registered Trademarks of DuPont.
Grafoil
®
is a Registered Trademark of UCAR Carbon Co. Inc.
O-ring Main Head Seal with
Retaining Lip
1
19
P a r r I n s t r u m e n t C o m p a n y
1 - 8 0 0 - 8 7 2 - 7 7 2 0
D e s i g n F e a t u r e s
